Estou com um problema programando no Python 3.8, o programa não executa

# -*- coding: utf-8 -*-
# fait par nadih - [Tradução em francês de (feito por nadih)]

# Projeto de Login e Painel de jogos com interface

# imports
from PyQt5 import QtWidgets, uic
import os


# functions
def chama_second_screen():
main_screen.label_4.setText("")
username = main_screen.lineEdit.text()
key = main_screen.lineEdit_2.text()
if username == "hidan" and key == "04021979fe":
main_screen.close()
second_screen.show()
else:
main_screen.label_4.setText("Dados de login incorretos!")


# logout's
def logout():
second_screen.close()
main_screen.show()


def wait_logout_msc():
wait_screen.close()
main_screen.show()


def wait_logout_ssc():
wait_screen.close()
second_screen.show()


# game def calls
def brawlhalla():
os.system("start steam://rungameid/291550")
second_screen.close()
wait_screen.show()


# variables and methods
app = QtWidgets.QApplication([])

# screens
main_screen = uic.loadUi("main_screen.ui")
second_screen = uic.loadUi("second_screen.ui")
wait_screen = uic.loadUi("wait_screen.ui")

# pushButton's and lineEdit's

# main_screen
main_screen.pushButton.clicked.connect(chama_second_screen)
main_screen.lineEdit_2.setEchoMode(QtWidgets.QLineEdit.Password)

# second_screen
second_screen.pushButton.clicked.connect(logout)
second_screen.brawlhalla_start_button.clicked.connect(brawlhalla)

# wait_screen
wait_screen.wait_logout_msc_.clicked.connect(wait_logout_msc)
wait_screen.wait_logout_ssc_.clicked.connect(wait_logout_ssc)


app.exec()